Fix for absent children prop in case of empty tree (#11128) (#11134)

packages/drivers/odsp-driver/src/compactSnapshotParser.ts

@@ -81,9 +81,11 @@ function readTreeSection(node: NodeCore) {
         if (records.value !== undefined) {
             assertBlobCoreInstance(records.value, "Blob value should be BlobCore");
             snapshotTree.blobs[path] = records.value.toString();
-        } else {
+        } else if (records.children !== undefined) {
             assertNodeCoreInstance(records.children, "Trees should be of type NodeCore");
             snapshotTree.trees[path] = readTreeSection(records.children);
+        } else {
+            snapshotTree.trees[path] = { blobs: {}, commits: {}, trees: {} };
         }
         if (records.unreferenced !== undefined) {
             assertBoolInstance(records.unreferenced, "Unreferenced flag should be bool");

packages/drivers/odsp-driver/src/compactSnapshotWriter.ts

@@ -60,9 +60,12 @@ function writeTreeSectionCore(treesNode: NodeCore, snapshotTree: ISnapshotTree)
         if (snapshotTree.unreferenced) {
             addBoolProperty(treeNode, "unreferenced", snapshotTree.unreferenced);
         }
-        treeNode.addString("children", true);
-        const childNode = treeNode.addNode("list");
-        writeTreeSectionCore(childNode, value);
+        // Only write children prop if either blobs or trees are present.
+        if (Object.keys(value.blobs).length > 0 || Object.keys(value.trees).length > 0) {
+            treeNode.addString("children", true);
+            const childNode = treeNode.addNode("list");
+            writeTreeSectionCore(childNode, value);
+        }
     }
 
     if (snapshotTree.blobs) {

packages/drivers/odsp-driver/src/test/jsonSnapshotFormatTests.spec.ts

@@ -0,0 +1,114 @@
+/*!
+ * Copyright (c) Microsoft Corporation and contributors. All rights reserved.
+ * Licensed under the MIT License.
+ */
+
+/* eslint-disable max-len */
+
+import { strict as assert } from "assert";
+import { IOdspSnapshot } from "../contracts";
+import { convertOdspSnapshotToSnapshotTreeAndBlobs } from "../odspSnapshotParser";
+
+const snapshotTree: IOdspSnapshot = {
+    id: "bBzkVAgAHAAAA",
+    trees: [
+        {
+            id: "bBzkVAgAHAAAA",
+            sequenceNumber: 1,
+            entries: [
+                {
+                    path: ".protocol",
+                    type: "tree",
+                },
+                {
+                    id: "bARA4itsHfCA5XZQaYhmASYpj",
+                    path: ".protocol/quorumMembers",
+                    type: "blob",
+                },
+                {
+                    path: ".app",
+                    type: "tree",
+                },
+                {
+                    path: ".app/.channels",
+                    type: "tree",
+                },
+                {
+                    path: ".app/.channels/23c54bd8-ef53-42fa-a898-413de4c6f0f2",
+                    type: "tree",
+                    unreferenced: true,
+                },
+                {
+                    id: "bARDoHhrwJMLoGao2yx8mD7nz",
+                    path: ".app/.channels/23c54bd8-ef53-42fa-a898-413de4c6f0f2/.attributes",
+                    type: "blob",
+                },
+                {
+                    path: ".app/.channels/23c54bd8-ef53-42fa-a898-413de4c6f0f2/d65a4af3-0bf8-4052-8442-a898651ad9b8",
+                    type: "tree",
+                },
+            ],
+        },
+    ],
+    blobs: [
+        {
+            id: "bARA4itsHfCA5XZQaYhmASYpj",
+            content: "   \n",
+            size: 4,
+            encoding: undefined,
+        },
+        {
+            id: "bARDoHhrwJMLoGao2yx8mD7nz",
+            content: "KR  \n",
+            size: 5,
+            encoding: undefined,
+        },
+    ],
+    ops: [
+        {
+            sequenceNumber: 2,
+            op: {
+                clientId: "38777331-8149-4d15-b734-cd8110295ab6",
+                clientSequenceNumber: 2,
+                contents: null,
+                metadata: {},
+                minimumSequenceNumber: 136505,
+                referenceSequenceNumber: 136505,
+                sequenceNumber: 2,
+                term: 1,
+                timestamp: 1657840275913,
+                type: "op",
+            },
+        },
+        {
+            sequenceNumber: 3,
+            op: {
+                clientId: "38777331-8149-4d15-b734-cd8110295ab6",
+                clientSequenceNumber: -1,
+                contents: null,
+                minimumSequenceNumber: 136505,
+                referenceSequenceNumber: -1,
+                sequenceNumber: 3,
+                term: 1,
+                timestamp: 1657840275922,
+                type: "join",
+            },
+        },
+    ],
+};
+
+describe("JSON Snapshot Format Conversion Tests", () => {
+    it("Conversion test", async () => {
+        const result = convertOdspSnapshotToSnapshotTreeAndBlobs(snapshotTree);
+        assert(result.sequenceNumber === 1, "Seq number should match");
+        assert(result.latestSequenceNumber === 3, "Latest sequence number should match");
+        assert(result.snapshotTree.id = snapshotTree.id, "Snapshot id should match");
+        assert(result.ops.length === 2, "2 ops should be there");
+        assert(result.blobs.size === 2, "2 blobs should be there");
+        assert(Object.keys(result.snapshotTree.trees).length === 2, "2 trees should be there");
+        const shouldBeEmptyTree = result.snapshotTree.trees[".app"]?.trees[".channels"]
+            ?.trees["23c54bd8-ef53-42fa-a898-413de4c6f0f2"]?.trees["d65a4af3-0bf8-4052-8442-a898651ad9b8"];
+        const emptyTree = { blobs: {}, trees: {}, commits: {}, unreferenced: undefined };
+        assert.deepStrictEqual(shouldBeEmptyTree, emptyTree, "Tree should have no blobs and trees");
+    });
+});